This is probably a good place to start:
Once you can decode the image (look at the example return data here: http://stackoverflow.com/questions/4332400/python-parsing-emails-with-embedded-images) then it's a matter of simply adding the image as an attachment.
One of the big issues you're going to run into is making this work with email from all email clients, as different clients use different formatting.
As far as uploading it as an attachment to the list, see this post:
And here's the code snippet:
foreach (FileInfo attachment in attachments)
FileStream fs = new FileStream(attachment.FullName, FileMode.Open, FileAccess.Read);
byte ImageData = new byte[fs.Length];
fs.Read(ImageData, 0, System.Convert.ToInt32(fs.Length));